Effects of short- and long-term TSH suppression on lumbar bone mineral density in both genders using PET/CT

Iatrogenic subclinical hyperthyroidism is induced intentionally in patients with differentiated thyroid cancer to reduce the risk of tumor recurrence. This retrospective study aimed to investigate the effect of thyroid-stimulating hormone (TSH) suppressive therapy on bone mineral density in men and women. Two cohorts of endocrine cancer patients were compared. In cohort A, 42 patients with long-lasting suppressed serum TSH were assessed. Cohort B consisted of 41 euthyroid patients. Bone density was measured in the L1-L4 lumbar vertebrae of all patients using PET/CT scans performed for cancer staging. In 17 patients of cohort A who received a second PET/CT scan, bone density was measured again to provide longitudinal analysis. A non-significant difference in age (p = .572) and equal distribution of sex (p = .916) was determined when comparing both cohorts. A significant difference (p = .011) with a moderate effect (η² = .08; 20.4%) was observed regarding higher bone mineral density (BMD^HU) in cohort B with normal TSH levels (M 160.63 ± 54.7 HU) versus cohort A under TSH suppression therapy (M 127.9 ± 59.5 HU) for a mean duration of 4.45 ± 2.64 years. Furthermore, no significant change in BMD^HU (p = .786) was found in those patients who received a second PET/CT scan after a mean observation time of 2.3 ± 1.2 years. In conclusion, long-lasting TSH suppression therapy caused a statistically significant decrease in BMD^HU while short-lasting therapy didn't. Therefore, we can assume a higher likelihood of osteoporosis in those patients under prolonged TSH suppression.